Testing the electrical characteristics of miniature devices, e.g., discrete semiconductor devices and integrated circuits, either alone or in combination, is a major undertaking in modern industry. It is common practice to test such devices several times during their manufacture and at least once after final assembly in a device package. To be competitive such testing should be done at a high rate of throughput and with acceptable reliability.
As the semiconductor art has progressed, the operating advantages of having components close together and the cost savings associated therewith have led to higher densities of components in a device. Such intense miniaturization results in smaller device terminals such as metallized pads being disposed very closely together. For example, a silicon chip may now have more than 70 pads, which may be about 0.002 inch wide with as little as about 0.001 inch between such pads. It will be appreciated that electrically contacting all such pads simultaneously and performing a series of tests successively through the contacts is a challenging task.
In addition to the miniaturization problem, the testing programs have become more complex and sophisticated. Previously, integrated circuit devices (ICs) may have had up to about 120 tests performed upon them, mostly with analog signals. Today, it is not unusual for a particular IC to further have more than 200 digital tests also performed upon it. Moreover, such testing may be done in from about 100 milliseconds to about one minute for each device. To execute such programs, the testing equipment has also become increasingly complex and more sophisticated.
For example, a modern test station may include an analog testing module in conjunction with a digital computer to perform a series of tests under A.C. or D.C. conditions. Because the computer is readily programmable, the test station may be readily adapted to new devices. However, such changes alone are often too generalized to suit a particular family of devices. Therefore, there is interposed between the test station and a device, a circuit board having passive and active elements thereon and usually including a number of relays for multiplexing between various parts of a device circuit or between parts of the test station. Such circuit board is referred to in the art as a performance board. The performance board and a paper tape containing specific machine programming may accompany the introduction of a family of devices from a design laboratory to a manufacturing line.
The number of electrical paths from a test station to a performance board is generally high and depends upon the type and number of tests desired for a family of devices. However, the number of electrical paths from a performance board to a device usually depends upon the number of terminals on the device itself. The impedance characteristics of such paths are of serious consequence to test results, particularly when making time measurements. Consequently, an effort is made to have the paths as short and uniformly spaced as is reasonably practicable.
One popular way of keeping such paths short and uniform is to utilize a probe card having a central axis projecting perpendicularly therefrom. A device to be tested is located near such axis, and probes and metal paths radiate therefrom to a circular array of contacts. A probe card is typically selected to suit the size of a device to be tested and the number and location of its circuit terminals. There are typically a large number of probe cards associated with a family of devices to be tested and such cards may often be changed because of wear, obsolescence or subtle changes in testing technique.
Between a probe card and a performance board there is generally provided a coupler adapter which accepts probe cards on a plug-in basis. The adapter is often connected to the performance board on a substantially permanent basis and provides electrical paths appropriate to the device and the capability of the performance board. Heretofore, most testing has required up to about 70 paths which could advantageously be accommodated by a coupler board in the shape of a ring having 70 pins which plug into and are soldered to a performance board. Such ring adapter provides rapid and inexpensive installation and electrical paths which are short and uniform in length and spacing. However, for more than 70 paths most conventional adapters are provided in the form of a circuit board wherein metal paths are provided from a circular array of sockets to accept the probe card to linear arrays of terminals for connection to a performance board. Consequently, the paths are generally nonuniform in length and spacing and connections to a performance board are expensive and wasteful of space thereon.
It is desirable to provide new and improved adapters to couple contacts on a card to elements on a circuit board. It is also desirable to provide adapters having electrical paths which are short and uniform in length and spacing. Such adapters should be readily coupled to a performance board with a minimum of expense and loss of space thereon. To the extent feasible, it is advantageous that the adapters take the shape of a ring having circular arrays of couplers such as sockets which coincide with arrays of contacts found on prior art probe cards.